The present invention relates to a data unit handling device and a method of controlling a data unit handling device.
In the field of communications the concept of packet based communication is well known. A data packet is a given length of data who's structure is determined by a given protocol, i.e. a set of rules governing the exchange, manipulation and interpretation of such packets. Depending on the protocol, different names are used, such as frame, packet, etc. A more generic term is protocol data unit (PDU), and the following description shall use the term “data unit” for simplicity, where this term “data unit” is to be understood generically as meaning any such finite data carrier, i.e. any packet, frame, etc.
Two implementations of a protocol at two points that exchange data units are also referred to as peers. A communication using data units will typically also employ the concept of layering. Layering means that different protocols are arranged in a hierarchical order, where the sending of data comprises the embedding of data units from higher layer protocols downwards to lower layer protocols, and the action of receiving comprises the opposite operation of reversing the embedding. The term “embedding” generically encompasses both encapsulation as well as segmentation. For example, FIG. 8 shows an example, where a protocol stack consists of implementations of an application layer L5, a transport layer L4, a network layer L3, a link layer L2 and a physical layer L1. In an example communication e.g. the application layer L5 passes down L5 data units (i.e. data units conforming to protocol L5) to the transport layer with L4, which embeds these L5 data units into L4 data units and passes them to the network layer L3, which embeds the L4 data units into L3 data units, etc. In such a communication, each layer shown in FIG. 8 will have a complementary receiving peer.
When the stack shown in FIG. 8 acts as a receiver, then received data units are passed upwards from the lower layers towards the higher layers.
The concepts of data units, protocol stacks, layering, etc. are well known in the art, see e.g. TCP/IP Illustrated, Volume 1, The Protocols, by W. Richard Stevens, Addison-Wesley Long Man, Incorporated, 1994. A further explanation is therefore not necessary here.